rtc: max77686: convert to devm_i2c_new_dummy_device()

I was about to simplify the call to i2c_unregister_device() when I
realized that converting to devm_i2c_new_dummy_device() will simplify
the driver a lot. So I took this approach.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20190830133124.21633-2-wsa+renesas@sang-engineering.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-max77686.c

@@ -690,8 +690,8 @@ static int max77686_init_rtc_regmap(struct max77686_rtc_info *info)
 		goto add_rtc_irq;
 	}
 
-	info->rtc = i2c_new_dummy_device(parent_i2c->adapter,
-					 info->drv_data->rtc_i2c_addr);
+	info->rtc = devm_i2c_new_dummy_device(info->dev, parent_i2c->adapter,
+					      info->drv_data->rtc_i2c_addr);
 	if (IS_ERR(info->rtc)) {
 		dev_err(info->dev, "Failed to allocate I2C device for RTC\n");
 		return PTR_ERR(info->rtc);
@@ -702,7 +702,7 @@ static int max77686_init_rtc_regmap(struct max77686_rtc_info *info)
 	if (IS_ERR(info->rtc_regmap)) {
 		ret = PTR_ERR(info->rtc_regmap);
 		dev_err(info->dev, "Failed to allocate RTC regmap: %d\n", ret);
-		goto err_unregister_i2c;
+		return ret;
 	}
 
 add_rtc_irq:
@@ -712,15 +712,10 @@ static int max77686_init_rtc_regmap(struct max77686_rtc_info *info)
 				  &info->rtc_irq_data);
 	if (ret < 0) {
 		dev_err(info->dev, "Failed to add RTC irq chip: %d\n", ret);
-		goto err_unregister_i2c;
+		return ret;
 	}
 
 	return 0;
-
-err_unregister_i2c:
-	if (info->rtc)
-		i2c_unregister_device(info->rtc);
-	return ret;
 }
 
 static int max77686_rtc_probe(struct platform_device *pdev)
@@ -783,8 +778,6 @@ static int max77686_rtc_probe(struct platform_device *pdev)
 
 err_rtc:
 	regmap_del_irq_chip(info->rtc_irq, info->rtc_irq_data);
-	if (info->rtc)
-		i2c_unregister_device(info->rtc);
 
 	return ret;
 }
@@ -795,8 +788,6 @@ static int max77686_rtc_remove(struct platform_device *pdev)
 
 	free_irq(info->virq, info);
 	regmap_del_irq_chip(info->rtc_irq, info->rtc_irq_data);
-	if (info->rtc)
-		i2c_unregister_device(info->rtc);
 
 	return 0;
 }